Articles of footwear have long been studied and redesigned to achieve enhanced comfort and performance. In this regard, and particularly in athletic shoes, primary concerns include the ability to provide the foot with a comfortable environment and to mitigate the shock or impact experienced when the shoe and, accordingly the foot and lower leg, impact the ground or floor. These forces are particularly significant during running and jumping. For example, a jogger landing on four or five square inches of the heel is estimated to absorb an impact force of about three to four times the weight of the jogger. Accordingly, a jogger of 180 pounds may create an approximate force of 720 pounds of shock on the heel landing area. Since each heel could impact the ground about 800 times per mile, it is easy to see the necessity of a shock absorbing mechanism in footwear.
In addition to a requirement that the shoe absorb intense and repeated impact, the criticality of comfort is readily understood by everyone who wears shoes. In fact, comfort in athletic shoes is known to effect the wearer's psychological state, and, therefore, his or her performance, muscular efficiency, energy consumption, and the athlete's ability to train and compete.
A great many shock absorbing devices exist in the footwear art to absorb the shock of foot strike and provide overall comfort. One common approach to impact absorption has involved using blocks of a compressible padding material. For example, shoes have been constructed with cotton padding, horsehair padding, rubber, plastic, foam, and the like. In these shoes, the inherent resilience of the compressible padding material is used to absorb and disperse impact. However, these materials are relatively inefficient in their ability to return energy to the shoe wearer, and after repeated use become compacted and lose their cushioning properties. Furthermore, on severe impacts, unless a relatively thick block of compressible padding is used, these designs experience full compression or “bottom out” quickly which results in severe impact stress on the wearer's body. When made thicker to avoid this problem, the compressible padding material becomes cumbersome and heavy and can interfere with the design of the footwear and an athlete's performance. In addition, when the padding material is thick, instability may be encountered.
Within the grouping of cushions constructed of compressible padding materials, foam inserts are preferred in athletic footwear because of their light weight and relatively favorable cushioning characteristics. Notwithstanding the superiority of foam within the compressible padding material group, it has been found that the cellular structure of a foam insert degrades with time and cyclic loading, resulting in collapse of the cell walls, and the corresponding rapid reduction in the cushioning characteristics of the insert.
Arguably, the preeminent foot wear cushion is a pneumatic device. As demonstrated by U.S. Pat. No. 259,092 (1882), pneumatic shoes sole have long been considered to be a superior form of cushioning. Notwithstanding this early effort, pneumatic cushioning devices failed for nearly a century, and for a variety of reasons, to achieve commercial success. In fact, until the inventions described in U.S. Pat. Nos. 4,183,156 and 4,219,945 were made, the art lacked the technological know-how to make pneumatic cushioning in shoes commercially successful. The inventions described in these patents revolutionized shoe design and the athletic footwear market place.
More particularly, the cushions described in these patents are well suited to absorb the impact experienced in athletic endeavors and effectively return energy to the athlete. Furthermore, the cushion is well suited to the intense and repetitious impact which occurs during athletic activities.
A pneumatic cushioning device having exceptional longevity can be achieved with a thick, strong, and durable elastomeric envelope. However, a thick envelope mitigates the benefits of fluid cushioning because the characteristics of the fluid are masked by those of the elastomeric barrier material. While it may be possible to form a better containment chamber using a very thick material, the competing interests of intrusive versus unobtrusive envelopes arises when a particular shaped cushion is desired. Moreover, fluids do not have an inherent shape. Therefore, the elastomeric material must assert shaping forces on the fluid. Obviously, a thick, strong elastomeric envelope can easily form complex shapes; however, the performing characteristics of the fluid medium are sacrificed. Accordingly, it is desirable to have a thin-walled envelope to obtain the maximum benefits of fluid cushioning.
Unfortunately, a thin, flexible envelope creates technical difficulty in providing long term retention of an inflatant gas. One alternative to address the loss of inflatant material has been to supply the cushion with a pump element to inflate and/or re-inflate the cushion. One example of this type of system is provided in U.S. Pat. No. 5,937,462 wherein a self-inflatable air cushion includes a collapsible plenum chamber connected to a main support chamber. When the plenum is collapsed by the foot, air is forced out of the plenum chamber, through a one-way valve, into the support chamber. While these types of systems work in theory, in practice, the complexity of a mechanical pumping system creates inherent failure possibilities.
Furthermore, a disadvantage associated with the tremendously successful use of air cushioning systems has been a reliance upon environmentally unfriendly fluorinated hydrocarbon gases which establish an activated diffusion system to maintain a pressurized cushion for many years. While extremely limited quantities are utilized, a negative public perception has become associated with their use. Accordingly, a desire exists to eliminate reliance upon these gases. The dilemma remains that, absent a completely perfect containment system, which has yet to be economically achieved, an environmentally acceptable gas containing cushioning system will at least slowly lose its pressurized inflatant gases.
The present invention provides an advantageous method and system for replenishing an inflatant material and avoids many of the disadvantages outlined above.
Throughout the specification, numerous references will be made to use of the cushion as a portion of the sole of athletic footwear; however, it should be realized that the inventive cushion can be beneficially incorporated into various types of footwear including, but not limited to, dress shoes, boots, sandals, etc. In addition, the cushioning device can provide protection in many types of athletic equipment where these unique cushioning and dynamic characteristics would be beneficial such as football, soccer, baseball, knee, leg, shoulder, neck and arm pads, saddles, helmets, gloves, seat cushions, etc.